Leaching behavior and mineral speciation of cement-solidified boiler fly ash from industrial waste incineration containing waste tires

This study characterizes the leaching behavior of fuel raw boiler fly ash (BFA) and cement-solidified/stabilized raw boiler fly ash (SBFA). X-ray diffraction analysis shows that the mineral composition of BFA is made up of anhydrite, calcite, and calcium silicate, whereas the composition of SBFA consists of quartz, calcium aluminum silicate, gypsum, and calcite. To verify the environmental impact of utilizing the SBFA material as a road base aggregate, standardized regulatory batch leaching tests are conducted on the SBFA sample, and the results indicate that the concentrations of Cd, Pb, As, Cr, and Ni are below the limits of determination, respectively. The column leaching tests results suggest that mineral solubility is the main factor affecting the release of major elements. Results of pH-stat tests show a decrease in the released-heavy-metal concentration even in extreme acid conditions (pH < 4) for the SBFA sample. Geochemical speciation modelling is performed on the leachate analysis results of the column experiment with PHREEQC. The results indicate that the main mineral composition of the SBFA material under the experimental conditions might consist of calcium compounds such as ettringite, portlandite, gypsum, and anhydrite.